DLARTGP
Originally DLARTG
November 2006
Adapted to DLARTGP
July 2010
November 2006
Adapted to DLARTGP
July 2010
Purpose
DLARTGP generates a plane rotation so that
[ CS SN ] . [ F ] = [ R ] where CS**2 + SN**2 = 1.
[ -SN CS ] [ G ] [ 0 ]
This is a slower, more accurate version of the Level 1 BLAS routine DROTG,
with the following other differences:
F and G are unchanged on return.
If G=0, then CS=(+/-)1 and SN=0.
If F=0 and (G .ne. 0), then CS=0 and SN=(+/-)1.
The sign is chosen so that R >= 0.
[ CS SN ] . [ F ] = [ R ] where CS**2 + SN**2 = 1.
[ -SN CS ] [ G ] [ 0 ]
This is a slower, more accurate version of the Level 1 BLAS routine DROTG,
with the following other differences:
F and G are unchanged on return.
If G=0, then CS=(+/-)1 and SN=0.
If F=0 and (G .ne. 0), then CS=0 and SN=(+/-)1.
The sign is chosen so that R >= 0.
Arguments
| F |
(input) DOUBLE PRECISION
The first component of vector to be rotated.
|
| G |
(input) DOUBLE PRECISION
The second component of vector to be rotated.
|
| CS |
(output) DOUBLE PRECISION
The cosine of the rotation.
|
| SN |
(output) DOUBLE PRECISION
The sine of the rotation.
|
| R |
(output) DOUBLE PRECISION
The nonzero component of the rotated vector.
This version has a few statements commented out for thread safety (machine parameters are computed on each entry). 10 feb 03, SJH. |